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    <p id="p1"><strong>左对齐</strong>:好好学习，天天向上。</p>
    <p id="p2"><strong>居中对齐</strong>:好好学习，天天向上。</p>
    <p id="p3"><strong>右对齐</strong>:好好学习，天天向上。</p>
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